Typically, for the production of ammonia in synthesis plants that operate in accordance with the Haber-Bosch process, use is made of ammonia reactors which, depending on the synthesis concept, contain up to three catalyst beds. The reactors consist of cylindrical pressure vessels and comparatively complicated internal constructions, the converter inserts, for receiving the catalyst beds and optionally heat exchangers. On account of the high pressure level of the synthesis of usually more than 200 bar, the diameters of the pressure vessels are kept as small as possible and the catalyst beds are arranged one beneath another along the container vessel axes. This arrangement has the consequence that the accessibility of the catalyst beds that are further away from the apparatus cover is highly restricted and filling with the catalyst material is rendered more difficult.
As a result of the different plant capacities and process engineering conditions, the catalyst beds have very different dimensions. On account of the efficiency with regard to the overall size and the pressure loss, the radial type of construction prevails nowadays, i.e. the catalyst beds are in the form of hollow cylinders and are flowed through in the radial direction.
In the case of continuous “hose loading”, as it is known, in which the reactor beds are filled with catalyst via one or more hoses, only average bulk densities that are beneath the required value for the synthesis reaction are achieved. Therefore, the catalyst beds have hitherto been filled using the batchwise stratified loading method, that is to say catalyst layers of 250-300 mm are introduced using a hose and subsequently compacted, by means of concrete vibrators and other vibrators, to the required bulk density of at least 2.8 kg/l of oxidized catalyst, or 2.3 kg/l in the case of pre-reduced, that is to say specifically lighter catalysts. The vibration of a layer can take more than an hour depending on the bed geometry.
This procedure is acceptable when new plants are filled for the first time, since the operations take place during preparation for start-up and are not on the time-critical path, that is to say do not result in expensive production stoppages.
However, during a catalyst change, the catalyst-changing operations usually take place on the time-critical path and can be decisive for the length of the downtime. For conventional catalyst-containing vessels, it is conventional in such cases to use the “dense loading” method, as it is known, to effect the desired bulk density in a continuous loading method without an interposed compaction step, and in this case the catalyst can be introduced in a correspondingly quicker manner.
In terms of phenomena, the difference in the achievable bulk densities between hose loading and dense loading can be explained in that during hose loading a large number of particles drop onto a small area in a short period of time, wherein the particles obstruct one another in the event of arrangement in a dense packing structure, whereas in dense loading a large number of particles drop onto a larger area in a short period of time, with the result that the particles have enough space and time to be arranged in a denser packing structure.
A large number of systems and methods for dense loading are known from the prior art. For example, US 2010/0019952 A1 describes, in which a rotating distribution system is arranged in the top of a catalyst vessel, said system distributing the dropping catalyst particles uniformly over the cross section of the reactor area, wherein the distribution system is fixed at the top. EP 1 152 967 B1 describes a similar system in which the speed of rotation of the rotating distribution system is adapted such that, as the level of the bed increases, the particles can still be thrown into the outer region of the bed without, however, striking the vessel wall.
U.S. Pat. No. 5,687,780 describes a system in which a rotating distribution system is likewise arranged in the top part of a catalyst vessel, said system distributing the dropping catalyst particles uniformly over the cross section of the reactor area, wherein the system can be displaced axially, however, thereby reducing the dropping height of the particles. EP 1 687 223 B1 describes such a system, which additionally operates with gas jets which drive the rotating distribution system and also influence the paths of the particles.
GB 2 287 016 A describes a system which is likewise arranged in the top of a catalyst vessel, said system distributing the dropping catalyst particles uniformly over the cross section of the reactor area, and in which the system can also be lowered and positioned in the reactor. The system is not rotatable and has vanes which project at different angles and which effect the uniform distribution of the particles.
These mentioned dense loading systems and also all further dense loading systems that are known from the prior art are not usable in ammonia synthesis reactors which are flowed through radially, since there is no top-side access and neither are the reactors which are flowed through radially able to be filled at all centrally along their axis of symmetry, since they are bounded on both sides in the radial direction by grid structures. Design details further constrict the clearances within the beds and thus impede accessibility for the loading systems. At the same time, specifically in reactors which are flowed through radially, it is particularly important for the particles not to be able to slip down during operation, since otherwise short-circuit currents would arise in the upper region of the radial bed.